Benzo[ c ]thiophene–C 60 Diadduct: An Electron Acceptor for p–n Junction Organic Solar Cells Harvesting Visible to Near‐IR Light

We synthesized a new 56‐π‐electron fullerene derivative through a Diels–Alder cycloaddition of benzo[ c ]thiophene that featured a relatively low temperature, closer to stoichiometric use of the diene, and easy product purification. The 56‐π‐electron benzo[ c ]thiophene diadduct ( BTCDA ) has a LUMO energy level of 0.09 to 0.18 eV higher than that of 58‐π‐electron fullerenes, and therefore, the BTCDA ‐based organic photovoltaic device exhibited a higher open‐circuit voltage and power‐conversion efficiency (PCE). When used with a binary‐donor system, including visible‐light‐harvesting tetrabenzoporphyrin ( BP ) and near‐IR‐harvesting titanyl phthalocyanine ( TiOPc ), the device had a PCE that was 1.5–3 times higher (2.8 %) than that for devices with BP or TiOPc alone because the binary‐donor device can utilize light between λ =350 and 950 nm.